A. Field of the Invention
The present invention relates to control systems for manipulator apparatus and more particularly to an improved control system for manipulator apparatus utilizing servo-loops that provide improved dynamic performance of the manipulator arm in a plurality of controlled axes by the use of variable inertia scaling and force feedback from the actuators of predetermined axes.
B. Description of the Prior Art
Various control systems for manipulator apparatus have been proposed and/or implemented utilizing servo-loops having command signals and feedback signals to position a manipulator arm controlled by a plurality of axes.
Control systems of this type, for example, are disclosed in U.S. Pat. Nos: 3,661,051; 4,086,522; 4,132,937; and application Ser. No. 154,439. The control system of U.S. Pat. No. 3,661,051 utilizes a servo-loop having position command signals and position feedback signals to control the manipulator arm. U.S. Pat. No. 4,086,522 utilizes position and velocity command signals, and position and velocity feedback in a servo control loop. U.S. Pat. No. 4,132,937 utilizes dynamic feedback including acceleration feedback and velocity feedback data that is combined with the position error signal to stabilize the control and operation of the manipulator arm by providing a high negative dynamic feedback signal during deceleration and a low signal during the acceleration phase to avoid conflict between the positional error signal and the dynamic feedback signal. Application Ser. No. 154,439 utilizes a servo-loop having position, velocity and acceleration command signals and position, velocity and acceleration feedback for control of the manipulator arm.
While the above prior art arrangements have, in general, been found satisfactory for their intended purpose, there is a continuing need in many manipulator applications for improved dynamic performance while maintaining servo-loop stability. Further, there is a need for improved dynamic performance of manipulator arm control where the manipulator arm experiences a wide variation in arm loads during performance of a work task.
Specifically, it has been found that control systems of the prior art are not optimized for the dynamic performance and load of the manipulator arm for the wide range of inertial loads that the manipulator arm experiences throughout its range of operating positions in the controllable axes. Thus in typical prior art control systems, servo-loop gains and loop parameters are dictated by stability requirements in accordance with the extremes of the inertial loads. Further it has been found that acceleration feedback is difficult if not nearly impossible to obtain for all controllable axes of a practical manipulator. Additionally, in many instances the acceleration feedback does not provide ideal feedback information as to the dynamic behavior of the manipulator arm. The control of the dynamic performance of the manipulator arm is further complicated by the change in working loads on the manipulator arm which varies from no load to full load for a given work task and which varies for various loads for different work tasks or during different steps in a work task.